The present invention relates to a transmission gear shift rod control device.
In particular, the present invention relates to a device for controlling the gear shift rod of a mechanical H type transmission normally used on motor vehicles and similar, and to which the following description refers purely by way of example.
As is known, currently used transmissions for motor vehicles and similar comprise a transmission casing from which projects at least one gear shift rod which is operated by the driver of the vehicle to select and engage a given gear.
In commonly used H transmissions, gear selection and engagement are effected by a combination of angular and axial displacements of the gear shift rod, from which the definition xe2x80x9cmechanical H transmissionxe2x80x9d derives.
With reference to FIGS. 1a and 1b, the gear engagement positions are in fact arranged in a double H configuration, in which the gears are divided into pairs (e.g. 1-2, 3-4 and 5-R) commonly referred to as xe2x80x9crangesxe2x80x9d, so that, as of a reference position normally located at the center of the double H, gear engagement is effected by axial (FIG. 1a) or angular (FIG. 1b) displacement, and range selection by angular (FIG. 1a) or axial (FIG. 1b) displacement, of the gear shift rod.
Currently used gear shift rod control devices substantially comprise a control shaft connected to the transmission shift rod itself; and a pair of actuators connected to and for rotating and axially moving the control shaft.
More specifically, when range selection is effected by angular displacement of the gear shift rod. (FIG. 1a), the actuator governing angular displacement of the control shaft provides for three different angular control shaft positions (four in the case of a six-speed plus reverse transmission), each corresponding to a given range selection; while the linear actuator governing axial displacement of the control shaft provides for three different axial control shaft positions, each corresponding to engagement of a given gear or to the neutral position. Conversely, when range selection is effected by axial displacement of the gear shift rod (FIG. 1b), the linear actuator governing axial displacement of the control shaft provides for three different axial control shaft positions (four in the case of a six-speed plus reverse transmission), each corresponding to a given range selection; while the actuator governing angular displacement of the control shaft provides for three different angular control shaft positions, each corresponding to engagement of a given gear or to the neutral position.
The above actuators are normally operated pneumatically, hydraulically or electrically, and are controlled by an electronic central control unit.
In another embodiment of the control device, the range selection actuator is replaced by a cam guide device which, when commanded, provides for combined angular-axial displacement of the control shaft of the device, so as to shift between two consecutive gears in two consecutive ranges, as opposed to two gears in the same range.
The cam guide device normally comprises a cylindrical cam fitted in axially rotating manner to the control shaft; and a lock device which, when commanded, prevents rotation of the cylindrical cam about the control shaft. The lock device is controlled by the electronic central control unit, and the cylindrical cam has a groove engaged in sliding manner by a radial pin extending from the control shaft. The groove is so shaped as to producexe2x80x94when the lock device is set to prevent rotation of the cylindrical cam about the control shaftxe2x80x94a combined angular-axial displacement of the control shaft to shift between two consecutive gears in two consecutive ranges.
Control devices with two linear actuators have the major drawback of requiring relatively complex component parts, such as multiposition actuators, valves, travel regulating members and position transducers, which call for accurate machining and involve high-cost construction arrangements. On the other hand, though much simpler in design, single linear actuator control devices provide for sequential shifting which, in certain operating conditions, is not particularly desired.
For example, when downshifting skipping one or more gears, single linear actuator control devices are forced to downshift through all the intervening gears, thus considerably increasing shift time and impairing the drivability of the vehicle. The same also applies to repeat shifting between first and reverse gear when parking, in which case the control device is again forced to shift continually through all the intervening gears.
It is an object of the present invention to provide a gear shift rod control device designed to combine the advantages of the two actuator solution with those of the single linear actuator, cam guide device solution.
According to the present invention, there is provided a control device for controlling the gear shift rod of a transmission, wherein the gear shift rod is movable, by virtue of axial displacements and/or rotations, between a number of gear engagement positions, each corresponding to engagement of a gear or to the neutral position; the control device comprising:
fixed supporting means;
a control shaft fitted to said fixed supporting means so as to rotate angularly about its own axis to effect a gear range selection, and move axially along its own axis to engage/disengage the gears; for each gear range, said control shaft also assuming three distinct axial positions corresponding respectively to an axial neutral position and two axial gear engagement positions;
actuating means for selectively moving said control shaft axially along its own axis between said three distinct axial positions; and
first cam guide means connected mechanically to said control shaft, and which provide, during axial displacement of the control shaft to shift between the two axial gear engagement positions of one range, for selectively effecting a sufficient angular rotation of the control shaft to shift to the immediately following/preceding range, so as to effect a sequential gear engagement, i.e. shift between consecutive gears in consecutive ranges; the control device being characterized by comprising second cam guide means connected mechanically to said control shaft, and which provide, during axial displacement of the control shaft to shift between the two axial gear engagement positions of one range, for selectively effecting rotation of the control shaft in the opposite direction to that effected by the first cam guide means, so as to shift between nonconsecutive gears.
Alternatively, according to the present invention, there is provided a control device for controlling the gear shift rod of a transmission, wherein the gear shift rod is movable, by virtue of axial displacements and/or rotations, between a number of gear engagement positions, each corresponding to engagement of a gear or to the neutral position; the control device comprising:
fixed supporting means;
a control shaft fitted to said fixed supporting means so as to rotate angularly about its own axis to engage/disengage the gears, and move axially along its own axis to effect a gear range selection; for each gear range, said control shaft also assuming three distinct angular positions corresponding respectively to an angular neutral position and two angular gear engagement positions;
actuating means for selectively moving said control shaft angularly about its own axis between said three distinct angular positions; and
first cam guide means connected mechanically to said control shaft, and which provide, during angular displacement of the control shaft to shift between the two angular gear engagement positions of one range, for selectively effecting a sufficient axial displacement of the control shaft to shift to the immediately following/preceding range, so as to effect a sequential gear engagement, i.e. shift between consecutive gears in consecutive ranges; said control device being characterized by comprising second cam guide means connected mechanically to said control shaft, and which provide, during angular displacement of the control shaft to shift between the two angular gear engagement positions of one range, for selectively effecting an axial displacement of the control shaft in the opposite direction to that effected by the first cam guide means, so as to shift between nonconsecutive gears.